Annually, 14,000 to 24,000 premature deaths are estimated to be associated with exposures to PM2.5, a mix of microscopic
particles less than 2.5 microns in size. A majority of these deaths occur in highly populated areas around the
state, including the South Coast, San Joaquin Valley and San Francisco Bay air basins.

"Particle pollution is a silent killer," said ARB Chairman Mary D. Nichols. "We must work even harder
to cut these life-shortening emissions by further addressing pollution sources head-on."

Particulate matter (PM) is a complex blend of substances ranging from dry solid fragments, solid-cores fragments
with liquid coatings, and small droplets of liquid. These particles vary in shape, size and chemical composition,
and may include metals, soot, soil and dust.

At the request of the board in 2006, ARB researchers carefully reviewed all scientific studies on the subject and
consulted with health scientists. While exposures to particulate matter have long been known as a serious health
threat, new information suggests that the pollutant is even more toxic than previously thought.

Hospitalizations, emergency room visits and doctor visits for respiratory illnesses or heart disease have been
associated with PM2.5 exposure. Other studies suggest that PM2.5 exposure may influence asthma symptoms and acute
and chronic bronchitis. Children, the elderly and people with pre-existing chronic disease are most at risk of
experiencing adverse health effects from PM2.5 exposure. Even small increases in PM2.5 exposures may increase health
risks.

While the new data reveals a greater threat from PM2.5, the state's previous efforts to reduce emissions throughout
the state have been successful. The ARB in coordination with the 35 air districts throughout the state continues
to develop and implement strategies of aggressive air pollution control. These measures have been so effective
for the last two decades that PM exposures have been reduced in California's major populated areas. Since the official
year-round monitoring of ambient PM2.5 began in 1999, concentrations have decreased 30 percent across California,
most notably in the South Coast and the San Joaquin Valley regions.

Additionally, in 2000 ARB adopted an aggressive risk reduction plan that targets all diesel PM sources in California.
As part of the plan, cleaner diesel fuels and new diesel engines (both on-road and off-road) have been developed.
In concert with regulations aimed at requiring cleaner new engines, other regulations have been adopted to address
diesel engines already on the road, including those in waste collection vehicles, transit fleet, school buses,
stationary engines, transport refrigeration units and portable engines. Later this year, ARB will consider rules
to significantly cut diesel particulate emissions from private truck fleets.

The Air Resources Board is a department of the California Environmental Protection Agency. ARB's mission is to
promote and protect public health, welfare, and ecological resources through effective reduction of air pollutants
while recognizing and considering effects on the economy. The ARB oversees all air pollution control efforts in
California to attain and maintain health based air quality standards.